Alarm fuse



A. DAVIS 2,923,796

ALARM FUSE Filed July 28, 1958 Feb. 2, 1960 INVENTOR. fier /0e C 0440.5

to be inserted into sockets in the base.

United States Patent O ALARM FUSE Arthur Chas. Davis, Newport Beach, Calif., assignor to Electrodyne Corporation, Santa Ana, Calif., a corporation of California 1 Application July 28, 1958, Serial No. 751,312

3 Claims. (Cl. 200-118) This invention relates to electrical fuses and deals more particularly with improvements in so-called alarm fuses.

Broadly speaking, an alarm fuse is an electricalfuse device which is equipped with means for signalling when the fuse is blown. This inventionis concerned with an alarm fuse of the type which is effective to energize an external alarm system when the fuse blows.

Briefly stated, the invention provides a fuse device equipped with a receptacle or base to be mounted on a wiring panel, and a plug-in type fuse unit having prongs When installed, these sockets are electrically connected toelectrical power leads and leads of an electrical alarm circuit in the man ner hereinafter described.

The fuse unit has a set of electrical alarm contacts which are designed to energize the alarm system. One of these contacts consists of a spring contact which is normally held away from the other alarm contact by the fusible element of the fuse.

When the current capacity of the fuse is exceeded, the fusible element parts and releases the spring alarm contact to complete the external alarm circuit.

With the foregoing preliminary discussion in mind, a

general object of the invention may be stated as being the provision of an improved alarm fuse of the character described.

A more specific object of the invention is the provision of an alarm fuse of the character described wherein the fuse element is completely enclosed so as to achieve suppression or elimination of arcing, eliminate any fire hazard, and prevent blowing of or damage to adjacent fuses when the fuse blows.

Another object of the invention is the provision of an alarm fuse of the character described having an internal flash barrier which acts to rapidly quench any are which is created when the fuse blows.

Yet another object is the provision of an alarm fuse of the character described which is readily replaceable.

A further object is the provision of an alarm fuse of the character described which is designed to replace the so-called grasshopper fuses presently used in telephone equipment without rewiring of the latter.

Yet a further object is the provision of an alarm fuse of the character described which is rugged in construction, relatively inexpensive to manufacture, and otherwise especially well suited to its intended purpose.

.Other objects, advantages and features of the invention will become readily apparent as the description proceeds.

The invention will now be described in detail by reference to the attached drawings, in which:

Fig. 1 is a view in perspective of the present fuse mounted on a wiring panel;

Fig. 2 is an enlarged section through the present fuse and showing the latter connected in external power and alarm circuits; and

Fig. 3 is an enlarged view in perspective of certain conductors embodied in the fuse.

- strip and alarm contact in 2,923,796 Patented Feb. 2, 1960 receive mounting screws for attaching the base to a wiring panel, for example.

Between the holes 14, the base has three openings in which are received three metal clips 16, 18 and 20, which provide and will be hereinafter referred to as electrical sockets or simply sockets. These sockets have ends or terminals 16a, 18a and 20a which extend beyond the rear face of the base, as shown, to connect to power leads and leads of an electrical alarm circuit.

Fuse unit 12 comprises a hollow body or case 22 of suitable electrical insulating material. As shown most clearly in Fig. 2, this case has a pair of end walls 24 and 26, an internal partition 28 parallel to the end walls, and a bottom wall 30. This partition thus divides the case 22 into two compartments. The open top of the case is closed by a transparent cover 32.

Tightly fitted in and extending to opposite sides of the bottom wall of the case are three conductors or conducting strips 34, 36 and 38. With this construction the strips 34, 36 and 38 are held in a given position with respect to the case 22. The case might comprise a molded plastic article, for example, which is molded directly about the strips.

The outer ends of these strips form flat prongs or lugs 34a, 36a and 38a that are spaced for insertion into the base sockets 16, 18 and 20. For reasons to be seen, strips 34, 36 and 38 will be referred to as a load strip, a common strip and an alarm strip, respectively. Similarly, the respective lugs will be referred to as a load lug, a common lug and an alarm lug.

As shown, the inner end of the load strip 34 lies flat against the inner side of case side wall 24. The inner ends of the common strip 36 and alarm strip 38 lie flat against the opposing sides of the partition 28 and the case side wall 26.

Joined at one end to the common strip 36, just above the bottom case Wall 30, is a spring contact strip 40 which serves as a movable alarm contact. This alarm contact is bent so as to normally engage a stationary alarm contact 42 on the alarm strip 38, as shown in phantom lines in Fig. 2. The stationary alarm contact 42 illustratively comprises a tab which is integral with and bent outwardly from the plane of the alarm strip.

Extending between the inner end of the load strip 34 and the free end of the alarm contact 40 is a current sensitive fuse means such as a fuse wire 44. The length of this fuse wire is such that so long as the wire is intact, the spring alarm contact 40 is held in its solid line position of Fig. 2, away from the stationary alarm contact 42. Clearance slots 46 and 48 for the fuse wire are provided in the partition 28 and common strip 36.

The ends of the fuse Wire 44 are joined to the load any convenient manner, as by solder. To facilitate soldering of the wire to the load strip and alarm contact, the latter are slotted and have edges thereof bent outwardly, as shown in Fig. 3.

In use, the fuse base 10 is secured to a wiring panel P (Fig. 2), for example. The socket terminals 16a and 18a are connected to a power lead 49, as shown, so that the fuse wire 44 is connected in series in the lead when the fuse unit 12 is plugged in the base. The socket terminals 18a and 20a are connected in an alarm .circuit 50, including a visual or audible alarm device 52 so the alarm contacts 40 and 42 of the fuse unit are connected in series in the circuit.

While the current flow through the power lead 49 is less than the current rating of the fuse unit, the fuse wire 44 remains intact. The spring alarm contact 40 is,

. 3 7 therefore, held away from the stationary alarm contact 42 and the alarm device 52 remains deenergized.

When the current in the power lead exceeds the current rating of the fuse unit, the excessive current flow through the fuse wire melts the latter. This results'in parting of the fuse wire and releasing of the spring alarm contact 40, which springs into engagement with the stationary alarm contact 42 to complete the alarm circuit.

Parting of the fuse element'of any fuse tends to cause arcing between the fuse conductors, especially in high voltage circuits. The complete enclosure of the fuse element or wire of the present fuse in the case 22 greatly reduces arcing time or eliminates arcing completely. This is due to compression of the air in the case, about the fuse wire, when the latter burns during blowing of the fuse.

This complete enclosure of the fuse wire also eliminates any possibility of ignition of inflammable material near the fuse and blowing or otherdamage to adjacent fuses when the fuse blows.

Partition 28 serves as a flash barrier wall which acts to rapidly quench any are that is created when the fuse wire parts. Thus, when the fuse wire parts, the alarm contact 40 springs away from the slot 46 in the flash barrier. This slot is made so narrow as to render it impossible for an are or flash that may be created at the instant of parting of the fuse wire to follow the alarm contact 40 as the latter springs away from the slot.

Accordingly, movement of the spring alarm contact 40 away from the flash barrier slot 46 breaks the electrical path created between that contact and the load strip 34 by the arc and the latter is extinguished or quenched. Since the arc is effectively contained in the large chamber below the flash barrier, as the fuse is viewed in Fig. 2, damage to the alarm contacts is prevented.

It will be seen, therefore, that the spring alarm contact serves the dual function of quenching any arc which is created when the fuse wire parts and completing the alarm circuit.

Transparent window 32 permits the condition of the fuse unit to be visually determined by observing the position of the spring alarm contact 40. In order to facilitate such visual observation, the end of spring contact adjacent the window may be painted a bright color so as to render the position of the contact more readily discernible.

Replacement of the fuse unit 12, when blown, may be readily accomplished by simply removing the old unit and plugging in a new one. Since all of the electrical conducting parts of the fuse are enclosed, accidental con tact of a worker with such parts is avoided.

It will be apparent, therefore, that there has been described and illustrated an alarm fuse which is fully capable of attaining the objects preliminarily set forth.

While a preferred embodiment of the invention has been disclosed, it will be apparent that numerous modifications in design and arrangement of parts of the in-. vention are possible within the scope of the following claims.

I claim:

1. An alarm fuse which includes: a hollow case of an electrical insulating material, said case having an open top and an internal partition dividing said case into two compartments, said partition having slot formed therein leading from said top; a common strip positioned within said case against said partition in one of said compartments, said common strip including spring contact means normally extending away from said partition; an alarm strip positioned within said compartment adjacent to said common strip, said alarm strip being capable of being engaged by said spring contact means in said extended position; a load strip positioned within said other compartment of said case; fuse wire means attached to: said load strip and said spring contact means so as to. hold said spring ,contact means away from said alarm strip, said fuse wire means extending through said slot.

, in said partition.

2. An alarm fuse which includes: a hollow case of an electrical insulating material; said case having an open top, ends remote from one another and an internal partition dividing said case into two compartments, each of said compartments containing one of said ends, said partition having a slot formed therein leading from said top; a load strip held within said case against one of said ends; an alarm strip held within said case against the other of said ends; a common strip held within the same compartment of said case as said alarm strip, said com-' mon strip being spaced from said alarm strip and including spring contact means capable of engaging said alarm strip when released; fuse wire means attached to said spring contact means and said load strip, said fuse wire means extending through said slot in said partition and serving to hold said spring contact means away from said alarm strip. I

' 3. An alarm fuse which includes: a hollow case of an electrical insulating material, said case having. bottom and a top, side walls, parallel ends positioned between said side walls and an internal partition located parallel to said ends between said side walls and between said ends, said partition having a slot formed therein leading from 'said top, an alarm strip positioned within said case, said alarmstrip including a prong extendingthrough said bottom wall, said alarm strip being located against one of said ends within said casing; a load strip positioned within said case against the other of said ends, said load strip including a prong extending through said bottom wall; a common strip positioned within said case against said partition on the side thereof adjacent tosaid alarm strip, said common strip including a prong extending through said bottom wall, said common strip including springcontact means capable of engaging said alarm strip when released; a fuse wire attached to said load strip and to said spring contact means of said common strip, said fuse wire extending through said slot in said partition, said fuse wire holding said spring contact means with respect to said common strip away from said alarm strip; and a transparent cover located on said top of said case, said fuse wire being visible through said cover.

References Cited in the file of this patent UNITED STATES PATENTS Miller et al. July 6, 1954 

